In an LTE (Long Term Evolution) system or an LTE-A (LTE-Advanced, Long Term Evolution Advanced) system, to increase uplink and downlink peak rates in the system, a CA (Carrier Aggregation) technology is introduced, that is, a plurality of contiguous or non-contiguous carriers is aggregated to simultaneously serve UE (User Equipment) when necessary, so as to provide a required rate. The CA technology may be used to maximize resource utilization and effectively utilize discrete spectrum resources.
Specifically, in the CA technology, a network device such as a base station may configure a plurality of operating carriers for each UE, where one carrier is a primary carrier, and the other carriers are secondary carriers. In addition, to maximize resource utilization, each secondary carrier may be configured in an unlicensed spectrum. The unlicensed spectrum generally refers to a common spectrum, that is, a spectrum that can be used by any organization or any individual. Therefore, generally, a rule of listening before transmitting needs to be followed in the use of the unlicensed spectrum, that is, a signal can be transmitted in the unlicensed spectrum only when it is detected that the spectrum is idle. In other words, if a secondary carrier is deployed in the unlicensed spectrum, the rule of listening before transmitting also needs to be followed in the use of the secondary carrier. Therefore, transmission in the secondary carrier may be discontinuous.
Specifically, for a non-contiguous carrier deployed in a spectrum such as an unlicensed spectrum, a base station may generally perform a CCA (Clear Channel Assessment) to assess whether a channel occupied by the non-contiguous carrier is idle, so as to determine whether the channel can be used. Generally, when the base station performs the CCA, a minimum duration of the CCA (which may also be referred to as a channel listening duration or a channel assessment duration) is not shorter than 20 μs. In addition, a maximum duration in which the base station transmits a signal by using the non-contiguous carrier every time cannot exceed 13 ms (that is, a maximum continuous channel occupancy duration of the non-contiguous carrier cannot exceed 13 ms). In addition, if the base station determines that the channel is not occupied by other devices for a long time, the base station periodically occupies the channel, where every two durations of occupancy by the base station may be separated by a CCA.
It can be known from the foregoing content that, for any UE, when there is a non-contiguous carrier in a plurality of operating carriers configured for the UE, there is a minimum duration of 20 μs (namely, a CCA duration) in which the non-contiguous carrier cannot transmit any signal. Although the CCA duration may occupy merely less than one symbol in a subframe, because the UE does not know a time point at which the CCA occurs, the UE cannot exclude the symbol occupied by the CCA from the entire subframe in which the CCA occurs. Consequently, no signal can be transmitted in 14 symbols of the entire subframe in which the CCA occurs, and resource utilization is reduced.